Robert I. Potter

Digital magnetic recording theory

A brief review of digital magnetic recording theory is given with emphasis on the analysis of ferrite, inductive thin film, and magnetoresistive heads. The utility of several approaches is demonstrated by three calculations: (1) resolution and signal amplitude of a shielded magnetoresistive head, (2) readback properties of a single sheet of permalloy with adjacent current conductor, and (3) analysis of spurious pulses generated by outside corners of ferrite heads. A discussion of high density digital recording is given, and it is concluded that the magnetoresistive head offers the greatest possible areal density of information. This density is conservatively estimated to be 1.6×107flux reversals per cm2(108per in2) at a head-medium separation of 0.125μm. Experimental data in support of this conclusion are given.

Modified mean‐field model for rare‐earth–iron amorphous alloys

A mean‐field model of the magnetic properties of amorphous rare‐earth–iron alloys has been developed which incorporates an Fe spin whose dependence on both the concentration and the species of rare earth is based on Mossbauer spectra. Using this model with a single fixed set of exchange constants, we have been able to calculate Curie temperatures which are in reasonable agreement with the data for amorphous rare‐earth (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu–iron alloys containing between 50 and 100 at.% iron. Better agreement with the measured Curie temperatures is achieved if the magnitudes of the Fe‐Fe and rare‐earth–Fe exchange constants are allowed to increase linearly with rare‐earth concentration. The latter case has the additional advantage of reproducing the observed shape of the magnetization‐vs‐temperature curves for wide range of composition and rare‐earth species.

Self-consistently computed magnetization patterns in thin magnetic recording media

A model involving head motion is given for self-consistently computing magnetic recording medium magnetization patterns. The reduction in demagnetizing field due to the presence of the high-permeability head structure is included, as is record head removal, read head replacement, and computation of the readback voltage. The model is capable of handling an arbitrary record current waveform. Optimum record-current amplitude for nonreturn to zero (NRZ) digital recording is first determined, and then single-, double-, and quadruple-transition computations are performed using two different values of hysteresis loop squareness M_{r}/M_{s} and both linear and exponential current reversals. Results are primarily for the Karlquist fringe field, but the recording properties of a head exhibiting regions in which the fringe field reverses sign are also briefly investigated.

Analysis of Saturation Magnetic Recording Based on Arctangent Magnetization Transitions

The minimum transition length for the arctangent magnetization transition is calculated. Readback voltage for the arctangent transition, where the magnetization contains components both in and normal to the coating plane, is calculated via the reciprocity theorem and Karlquists fringe field equations. Several misconceptions currently existing in the literature are discussed.

Self-consistent computer calculations for perpendicular magnetic recording

A comparison of perpendicular and longitudinal recording indicates that conventional heads are suitable for recording on high coercivity media having perpendicular magnetic anisotropy. At equal bit shift and head to disk separation perpendicular recording gives a factor of 2.5 increase in the linear density attained with media in use today.

Exchange coupling in amorphous rare earth‐iron alloys

The technologically important amorphous rare earth (RE)-transition metal (TM) alloys provide an excellent system for investigating basic magnetic phenomena in amorphous magnetic materials. The sensitivity of the magnetic properties of the amorphous RE-TM alloys to slight compositional changes indicated the need for a rapid survey of the systematic variation of their properties. A brief review of this survey and the theoretical models is presented. One result is to point out Fe as the most favorable TM for obtaining a more detailed understanding of the magnetic properties. Data are presented from /sup 57/Fe Moessbauer effect, magnetometer and magneto-optic measurements on amorphous RE(Gd, Tb, Dy, Ho, Tm, Yb, Lu)-Fe amorphous alloy films. The Moessbauer effect results indicate that the Fe spin decreases with increasing RE content but the rate of decrease is dependent on the RE effective spin, (g - 1)J. A mean field theory model is presented which reasonably reproduces the magnetic properties of the amorphous RE--Fe alloys, and which provides useful insights into their properties. 9 figures, 30 references.

A self‐consistent calculation of the transition zone in thick particulate recording media

We describe a fully two dimensional self‐consistent calculation of an isolated transition in a thick particulate magnetic recording tape. The calculation includes relative motion between the tape and head, as well as a vector magnetic hysteresis model.

Analytic expression for the fringe field of finite pole-tip length recording heads

Previous computations based on a conformal transformation are used as a guide in selecting a plausible magnetic scalar potential at the surface of the head. An analytic expression for the horizontal component of the field is obtained from this potential. Certain characteristics of the potential and field are discussed.

Improvements to a self-consistent model for the magnetic recording properties of non-particulate media

Three aspects of self-consistent calculations are considered. The first includes various numerical techniques for reducing by a factor of 60 the running time of the original program. Second, a detailed treatment of the recording characteristics of the thin film head is given. Third, the model is expanded to two dimensions and used to compute with head motion the magnetization vector in a Fe 3 O 4 storage medium of moderate thickness. The role of this usually neglected out-of-plane magnetization component is discussed.

A vector model for magnetic hysteresis based on interacting dipoles

A model for magnetic hysteresis is described in which the applied field intensity is free to rotate as well as vary in magnitude. The model is an infinite lattice of ellipsoidal Stoner-Wolfarth particles with N^{3} = 8,27,64,125,216... independent and not necessarily identical particles per unit cell. Techniques for making this simple yet very general model computationally tractable are described. The model is intended primarily for studying the magnetic recording process in particulate storage media.